1. Field of the Invention
The present invention relates to an industrial oven which heats product by circulating air internally through the oven, and more particularly, to an industrial oven which enables air to flow in a continuous, reversible path by opening and closing vent doors arranged in a particular configuration, wherein the paths are substantially symmetric.
2. Discussion
Reversible air flow, industrial ovens have long been used for heating, reheating, preheating, precipitation, hardening, and homogenizing, annealing and curing a varied assortment of products. The reversibility of air flow is typically desirable because when heating a product to a predetermined temperature in an air flow oven, a temperature gradient forms across the product with the upwind edge of the product obtaining a substantially higher temperature than the downwind edge. The temperature gradient forms because the air flow loses heat as it traverses the product.
While the use of the reverse air flow oven is particularly desirable, several characteristics of the, prior art reverse air flow industrial ovens prove to be somewhat undesirable. For example, present reverse air flow ovens fail to provide symmetric heating profiles for each direction of air flow. Typically, one direction provides a suitable heating profile, while the opposite direction exhibits a substantial decrease in the heating profile. Often, this decrease in the profile may be twenty percent or higher. Further, because it is desirable to provide a substantially symmetric path for the air flow, Present reverse air flow ovens route the air flow non-symmetrically about the product by reversing of the air circulation mechanism, such as a fan. This inherently leads to asymmetric profiles even though the air flow path may be symmetric. The asymmetric profile results from the air circulation mechanism, the fan, having a diminished capacity to move air in one direction verses the other.
Reversing the air circulation mechanism can also result in other considerations becoming more relevant. In particular, power usage and the process of reversing the air flow must be carefully examined. For example, the volume of air circulating in large industrial ovens necessarily requires circulation fans of substantial size which draw substantial amounts of electrical power. Reversing such fans also necessarily requires substantial energy in order to effect dynamic breaking of the fan and additional substantial energy in order activate the fan in the reverse direction. The electrical requirements not only consume considerable electrical energy, they often necessitate installation of specialized circuitry to carry out. When the fans are deactivated in order to reverse the direction of the fan and thus the air flow becomes much more relevant. The air flow proper heating of the product. For example, when the fan is slowed in preparation for reversing its direction, the heat source for the oven must also be deactivated so as to not generate hot spots near the heat source because air in proximity to the heat source becomes temporarily stagnant. When the fan is reactivated in the reverse direction, reactivation of the heat source must typically be in accordance with the air flow as the fan ramps up to full speed. Existing air flow ovens take approximately 11/2 minutes to stabilize during this air flow reversal process. It is generally desirable to reverse the air flow frequently. However, because of the above considerations, existing air flow ovens often reverse air flow only every hour. This results in a substantial heating of product in the upwind section of air flow and substantially diminished heating of the product in the downwind portion of the air flow. Thus, it is the object of the present invention to provide a reverse air flow oven which provides a symmetric heating profile along the product, regardless of the direction of air flow.
It is a further object of the present invention to provide a reverse air flow oven in which the air flow may be reversed by directing the air flow through duct work, rather than reversing the direction of the circulation fan.
It is yet a further object of the present invention to provide a reverse air flow oven in which air flow may be reversed frequently with a minimum input of electrical energy and a minimum stabilization period.
It is yet a further object of the present invention to provide a reverse air flow oven in which the air flow is substantially symmetric with respect to the product.
It is yet a further object of the present invention to achieve uniform heating and temperature uniformity in the air stream by uniformly distributing the air over a duct face which contains a mechanism for distributing the air and velocity pressure.